An active matrix-type liquid crystal display apparatus such as a liquid crystal display uses thin film transistors (hereinafter referred to as TFTs) as switching elements and is constituted by transparent pixel electrodes, wiring portions such as gate wiring and source/drain wiring, a TFT substrate that includes a semiconductor layer composed of amorphous silicon (a-Si) or polycrystal silicon (p-Si), a counter substrate that includes a common electrode and is arranged so as to face the TFT substrate with a particular distance therebetween, and a liquid crystal layer filling the gap between the TFT substrate and the counter substrate.
Aluminum (Al) alloy films have been used as a wiring material of gate wiring and source/drain wiring of a TFT substrate. However, as the size of the display devices increases and the image quality improves, a problem of signal delay and power loss attributable to high wiring resistance has become noticeable. Thus, copper (Cu), which has a lower resistance than Al, is gathering much attention as a wiring material.
When pure Cu or a Cu alloy (hereinafter generally referred to as Cu-based alloys) is used as a wiring material, a barrier metal layer composed of a refractory metal such as Mo, Cr, Ti, or W is usually interposed between a Cu-based alloy wiring film and a semiconductor layer of a TFT as described in PTL 1 to 7. This is mainly due to the following two reasons.
First, if a Cu-based alloy wiring film is directly brought into contact with a semiconductor layer of a TFT without using a barrier metal layer, Cu in the Cu-based alloy wiring film will diffuse into the semiconductor layer due to the heat history in the subsequent step (e.g., step of forming an insulating layer on the TFT or a heating step involving sintering or annealing) and thus the TFT characteristics are degraded or the contact resistance between the Cu-based alloy wiring film and the semiconductor layer is increased.
Second, when Cu in the Cu-based alloy wiring film diffuses into the semiconductor as described above and a reaction layer between the semiconductor layer and Cu is formed, the Cu-based alloy wiring film becomes detached from the semiconductor layer at this reaction layer, which is a problem. In other words, bringing the Cu alloy film and the semiconductor layer into direct contact with each other decreases the adhesion.
However, in order to form such a barrier metal layer, a system for forming a barrier metal is needed in addition to the system for forming Cu-based alloy wiring films. In particular, a film-forming system equipped with an extra film-forming chamber for forming barrier metal layers (typically, a cluster tool in which a plurality of film-forming chambers are connected to transfer chambers) must be used, and this increases the production cost and decreases the productivity.
Under this circumstance, PTL 8 describes a technology that does not use such a barrier metal layer. PTL 8 discloses a direct contact technology for a Cu-based alloy film and a semiconductor layer, and describes a wiring structure composed of a material including a Cu-based alloy film and a nitrogen-containing layer or an oxygen-nitrogen-containing layer, where N (nitrogen) in the nitrogen-containing layer or nitrogen or oxygen in the oxygen-nitrogen-containing layer is bonded to Si of the semiconductor layer.